Grid glow tube



3, 1936. w. E. BAHLS 2,033,689

GRID GLOW TUBE Filed Aug. 20, 1932 2 sheets-sheet 1 WITNESSES: INVENTOR c? a Nafej Bah [5. fl

W. E. BAHLS GRID GLOW TUBE March 3 193% zmm 2 Sheets-Sheet 2 Filed Aug. 20, 1932 l N\ IENTOR Wa/fer. E Bah /s WITNESSES @rv/C M Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE GRID GLOW TUBE Pennsylvania Application August 20, 1932, Serial No. 629,657

8 Claims.

- This invention relates to space-current devices, and particularly to that type of space-current apparatus in which an ionization current is controlled by a grid.

It is an object of my invention to render the operation of such devices more certain.

It is a further object of my invention to prevent a discharge between the cathode and any portion of the control electrode or its support except the portion which is directly depended upon for the control of the space current.

It is a further object of my invention to insert a barrier between the cathode and the support for the control electrode and thereby prevent a discharge from the cathode directly to said support.

It is a further object of my invention to provide a cap enclosing the portion of the grid support which extends above its sleeve and also enclosing the portion of the grid directly connected to said support.

It is a further object of my invention to prevent an are or glow discharge reaching the Welded connection between grid and grid support.

Other objects of my invention and details of the structure will be apparent from the following description and the accompanying drawings in which the Figure 1 is a vertical section of a gridglow tube embodying my invention and Fig. 2 is a modification of Fig. 1.

A description of the grid-glow tube to which my invention has been applied and of the circuit with which such tube is used will be found in the application of Dewey D. Knowles, Serial No. 564,267, filed September 22, 1931, assigned to the Westinghouse Electric and Manufacturing Com- P y- My invention resides in the features herein described which have been added to the gridglow tube disclosed in said application of Knowles, but it is not limited to this particular form of space current device. It may be added to any other forms of space current device and to other circuits.

In the drawings, an envelope l encloses a space which has been evacuated and filled to a small pressure with a suitable gas. The envelope is provided with a press 2 in which are mounted the cathode 3, anode 4, grid support 5 and anode shield 6, all of which are described in greater detail in said application of Knowles, and the detailed description thereof is not repeated here because my invention does not reside in any of these features.

Upon the grid support 5-agrid I0 is secured in any desired mannerpreferably by means of a Weld indicated at H. The portion of the grid l0 which extends to the weld ll constitutes an arm supporting the ring-shaped portion l2 which is coaxialwith the anode 4 and spaced a small distance therefrom. The ring i2 is the part of the grid which is relied upon to control the electrostatic field in the neighborhood of one end of the anodet. The remainder of the grid serves only as a mechanical support and as a conductor to unite the ring l2 to the support 5 and, by the connection of this support through the press, with the external source of grid potential.

A shield or cap l3 surrounds the top of the grid support 5 and substantially all of the arm II]. An opening [4 in the shield l3 permits the arm ID to project therethrough and thus permits the ring l2 to be located in its proper position.

2 The cap 13 is supported in any suitable man- 0 ner. It may be mounted upon the upper end of the sleeve l5 which surrounds the grid support 5, either by means of friction or by providing a shoulder at the upper end of the sleeve. Another method of support, which I have chosen as the form for illustration, connects the cap l3 with the cathode 3. An ear l6 integral with the part of the cap which encloses the top of the sleeve is connected to a rod or wire I! which is welded to one of the supports of the cathode, as shown at l8. When supported in this way, the cap must be of insulating material.

Instead of a direct connection between the cap 13 and the cathode 3, as in Fig. 1, the wire I! may extend through the press as disclosed in Fig. 2 and provision may be made external to the tube for impressing a diiference of potential between the cathode and the cap. The connec-- tion should also include a high resistance 20. When such provision for an externally im-- pressed potential is made, the cap I3 should be of metal as illustrated in Fig. 2.

Another alternative is to support the cap by a lead similar to the lead H, but extending to the support for the shield 6. The high resistance illustrated in the above-mentioned application of Dewey D. Knowles will then limit any current to or from the cap.

In the operation of the device, the tube is mounted in the usual way to constitute apart of a circuit by which a dilference of potential is established between the anode 4 and the oathode 3. When this difierence of potential is sufficient and is directedfronrthe anode toward the tential to transfer the discharge is the explacathode, current will flow by an are or a glow discharge between the two, provided the potential upon the ring l2 does not prevent. The circuit is so arranged that a potential is impressed through the standard 5 and arm l0 upon the ring l2.

The potential upon the grid must be positive relative to the cathode by morethan, a characteristic amount before the discharge betweencathode and anode will occur. In some tubes to which this invention has been applied the anode.

is some 200 volts positive relative to thecath ode and the tube will not become conductive unless the grid potential exceeds 384 voltsrelative to the cathode.

The circuit conditions are such that'when the tube is to become conductive, a potential exceeding the characteristic. potentiai is im; pressed upon the ring 12.

Heretofore, it has happened that, when the difierent of potential between the cathode 3and the grid l2 was sufiicient, a discharge occurred between the cathode and some portion of the grid other than the. ring l2. Discharges from the cathodeto the welded joint H are particularly likely' to occur. Thenature of the grid structure,particularly the materials chosen, and the nature of the gas conditions, particularly the kind of gas used, have an influence on the likelihood of such afdischarge occurring.

If'a'dischargefbetween the cathode 3 and the weld flforibetween the cathode and the grid support 5, or the arm lfl, occurs, and in tubes noteq'uipped' with a'shield l3, such discharges frequently occur,v a much greater difference of potential'betweenthe anode; and the cathode 3 is r ei ii' fshifi e isp e l rqm h i to the anode than is necessary if the discharge between cathodei'andgrid stothering l2. This A change in the required value of the an0de -p0.-

nation of the erratic behaviour of such tubes under these co nditions, V

Whenla discharge occurs from the cathode to the ring I2, an anode potential very slightly greater than that sufiicient to maintain a discharge between cathode and anode is sufficient tol cause the prompt transfer of the discharge frqmthe ring to the anode. Inone tube, actuaily built and tested, in which 200 volts were required to maintain the discharge between cathode and anode, the tube remained non-conductive until the grid potential was 384 volts abovethe cathode. Then adischargeto the ring was transferred at once tOy the anode. In a similar tube without a shield 13, when the dis-v charge became concentrated at the weld II, the.

anode potential had to be increased to 700 volts above the cathode before the discharge would transfer to the anode.

When the housing I3 is provided, it presents a barrier separating the cathode 3 from the standard 5, the weld H and the arm 10. A discharge from the cathode to any of these parts is thereby prevented. 'A discharge directly from the housing 13 to any of these parts will not occur be cause thedistance between the housing and any of them is smaller than the mean free path of the gas within the tube. V A discharge from the cathode a through the opening to the weld u of a discharge to the ring l2. When such a discharge occurs, it will transfer to the anode 4 iminediately, provided the anode potential is slight- 1y greater than that necessary to maintain the discharge and the tube thereafter conducts from anode to cathode in the regular way until the anode potential is reduced to a value which will not maintain the discharge.

When-the source of potential in-the circuit associated with the tube is alternating, the conductivity of the tube can be controlled by controlling t e hase of the potential impressed upon the grid. In this Way the moment within the positivev halfecycle at: which the tube will become conducting-is controlled, and the average value of--the current through the tube throughout the cycle is thus controlled. If discharges occur between thaanode;andlthe weld II, as above described, the, current through the tube will no longer havea predictable relation to the phase of the grid potentiaLbutthere wil-l. be. transition points,- that-is, poi'ntsof adjustment of grid phase. at-whiclrthefbehavoir,of the tube is difierentv from that intended.

The introductionof theacap l3 preventsdischarges to theweld; ll and'the Welded partsland thus prevents ,such transition points.

My invention ,is capable ofmany modifications which, will readily occur to those skilled in the art... For example,,the cap l3 maybe-made of insulat-v ing material, as in Fig. 1 or of conductingmaterial as-in Fig. 2, and when conducting, ;.a control potential.- may be impressed upon'it. The omission of; specificmentionv of such modificafi tions is not tobe regardedas indicating an intentional limitation. The only limitations intended. are those required bythe prior art orindicated in the accompanying; claims.

I claim .as .my invention 1. In a grid-glow; tube, a-.control-electrode sup; 40., port, a control-electrode comprising ,.a member in efiective positionior control; of, the. space-current and an, arm;;whe reby.; said .member is. supported. from said control-electrode support, and as,- cap 1. mounted oversaid support and. surroundingsai'd 45;; armin closely spaced. relation thereto..:

2. h controhelectrode assembly. comprising.- ;a conductive suppor t,.a.sleev e .enclosingasaid sup-s. port,,an arm securedat.oneendto.saidisupport and a cap enclosing said-garmexceptua.portiontO. ati s. free nd; 7

3.; A controlelectro,de.;zassembly comprising a conduqtil e supnortgalsleeve .enclosing;said sup-. rt. ana tmsecured at. one. end. to said support; aringmn h eend of said armtandza cap en-.

closing sj ;excent for thefree. end containing said ring.

4., A;1controL- electrode. assembly -1.comprising-. a nductive upport. .a sleeve. enclosing. said. sup-2 port, an arm :secured. at one ,end .to. said support, a r nezpn the; freeendof; said arm-.and a .cap. support,on said; .s1eeve enclosing said arm except for theirqe;;,end,;containing; said. ring, said sup-1 port, arm and ring being;.insulated zbysaid .cap: and s eeve...

5.;A ,;gaseous discharge, device comprising; an anodeuaqcathode a 3001113101 electrode having. a portion; adjacent said; anode, andaconductive shield;.aboutitheexposed portion of said control electrode not; included; in: the first-mentioned rtionadjacent saidianode. 1

.6. A gaseous. .discharge. device: comprising .a pointed-anode, a cathode of .large area -surround.-. ing said anode, a controlgelectrodeintermediate saidanodeand cathode and;.having .a portiorrad- 752 jacent said anode and a conductive shield about the exposed portion of said control electrode not included in the first-mentioned portion adjacent said anode.

7. An electric discharge device comprising a container, an anode, cathode and control electrode therein, said control electrode having an efiective portion closely adjacent said anode and a shield spaced from said control electrode but closely surrounding the control electrode except for the effective portion thereof adjacent said anode.

8. An electric discharge device comprising a container having a gaseous medium therein, a first electrode, a second electrode, a third electrode, intermediate in position between said first and second electrode, an auxiliary electrode enveloping the major portion of said first electrode and an auxiliary shield screening all except a small portion of said third electrode from all the other said electrodes WALTER E. BAHLS. 

